1. Field of the Invention
The present invention relates to CMOS amplifiers, and more particularly concerns a CMOS buffer reference amplifier uniquely adapted for driving a large switched capacitative load. Although the present invention has a variety of other applications, it has been particularly designed for use in a compensation circuit of an imaging device in which invisible infrared light from a scene is employed to provide a visible light image that replicates the scene.
2. Description of Related Art
Night vision devices have been available for many years. One category of these conventional night vision devices uses image intensifier technology. This technology is effected using a device generally known as an image intensifier tube. These image intensifier night vision devices require some residual light, such as moon or star light, in which to operate. This light is generally rich in near-infrared radiation, which is invisible to the human eye.
Another category of conventional night vision device is represented by the cryogenically cooled focal plane array thermal imaging devices. These devices use a photoelectrically responsive detector which is cooled to a temperature in the cryogenic range to reduce unwanted thermal noise.
A significant disadvantage of this category of night vision device is the requirement for cryogenic cooling of the detector. However, such coolers require a considerable amount of power, are not without their own maintenance and reliability problems, and are generally noisy.
Image intensifier systems, focal plane array systems, infrared imaging systems of the type described below, and many other types of systems include extensive signal processing circuits that employ reference circuits designed for large capacitative loads. For example, such commonly used circuits as groups of digital to analog converters used in certain signal processing of imaging systems often employ large banks of switched capacitors for establishing voltage levels. Drivers for such large capacitative loads have usually employed bi-polar design techniques. Designs employing CMOS circuitry have exhibited inadequate performance. Prior capacitative load driving circuits fail to have sufficiently low quiescent current, particularly when required to provide high output peak currents for large capacitive loads. Settling times have been unsatisfactory, which may limit speed of operation.
Accordingly, it is an object of the present invention to provide a voltage buffer amplifier that avoids or minimizes above-mentioned problems.
An additional object is to provide such an amplifier having a fast recovery time when employed with a large capacitative load.
Still another object of the invention is to provide a voltage reference for a large capacitative load of an imaging system that has low quiescent current.